3 replies to this topic

[R Williams]

Hello all,

 

I have a chemical injection pump application with a Swagelok R3A proportional relief valve installed on the pump discharge. With reference to the flow curves given in the Vendor catalogue for liquid service, these are referenced to water. In my application I am pumping a high viscosity chemical (300cP at normal operating temperature). Can these curves be directly used for fluids with higher viscosities, or is there some form of correction required (analogous to API type viscosity correction)?

 

For info, I have used the API 520 Part I sizing equations with viscosity correction. However, as the viscosity is high and flowrate is very low the viscosity correction factor is also <<1. This result in predicting the installed valve to be undersized. I am doubtful that these equations are suitable for this application given the proportional nature of the valve.

 

Any help greatly appreciated.

 

Rhys Williams

 

[Dazzler]

Hello Rhys, 

 

I've seen and used these valves on small systems but not high viscosity.

 

If you think of the valve like we do a centrifugal pumped piping system, if the flow increases then the pressure drop will rise. I think it can be argued that for a more viscous fluid, its pressure drop through a system will be higher than for water, trouble is that at this higher pressure drop, flow is likely to lower.

 

In other words, I suspect that if you want a certain flow through the RV at a certain % open (say fully open) then a higher pressure drop will be needed across the RV for a viscous fluid. If the outlet pressure is perhaps relatively low and constant, then you will need a higher inlet pressure to achieve the higher dp. However if the inlet pressure is the opening set pressure which you do not want to change (protects the system), then this means the flow will be lower because you haven't given it a higher dp to counteract the higher viscosity.  To quantify this you may need to look at the fluid flow equations for liquids. and how the dp changes with viscosity.  Watch out also that they will be for "Newtonian" fluids.

 

Dazzler

Edited by Dazzler, 23 March 2019 - 01:26 AM.

[latexman]

It may be worth asking Swagelok if they have a viscosity correction for those valves.

 

Please let us know what you find out.

Edited by latexman, 25 March 2019 - 06:16 AM.

[Chemitofreak]

I agree with Latexman, check with the vendor